(i) Field of the Invention
The present invention relates to a fixing board for fixing an optical data bus comprising a long plate of a light transmissive material having one side formed into a step-wise configuration and signal light incoming/outgoing areas formed by sloping each end surface of each step approximately at 45 degrees in relation to the plate surface, and relates to an optical back plane board using the fixing board.
(ii) Description of the Related Art
To improve the processing performance of a signal processing unit, which employs a parallel architecture comprising a back plane board (mother board) and a plurality of nodes (daughter board), enhancement of the bandwidth by increasing the speed of transmission through a bus and bit multiplication has been sought.
Although further speed increase is required for such a signal processing unit employing a parallel architecture, the achievement of further speed increases using a conventional electrical wiring requires a circuit board design for reducing noises and delay with respect to the mother board and the daughter board. Optical fiber interconnection also has been introduced for increasing speed, even though it leads to further complicated wiring.
While increasing speed of a signal processing unit by the conventional electrical wiring is sought, increasing speed of a signal processing unit by intra-system optical interconnection technology called optical interconnection has been considered. As the outline of optical interconnection technology is described, for example, in The Transactions of the Institute of Electronics, Information and Communication Engineers, Vol.79 (No.9), September, 1996, xe2x80x9cOptical Interconnection Technology and its Applicationsxe2x80x9d by Osamu WADA, pp.907-909 and in Journal of Japan Institute of Electronics Packaging, Vol. 1, No.3 (1998), xe2x80x9cToward New Computing Systems with Optical Interconnectionxe2x80x9d by Masatoshi ISHIKAWA, pp.176-179, various forms may be proposed depending on the configuration of a system.
However, when optical interconnection utilizing optical fibers as a signal transmission medium is introduced not only into systems for industrial use but also into systems commonly used in offices and homes, there are problems, such as high packaging cost due to need for accurate positioning of optical connections and difficulty in realizing interconnection of multiple nodes with a simple structure.
As technology to solve these problems, an optical data bus 50 as shown in FIG. 6 was proposed at The 25th Symposium on Optics, 2000, Lecture No. 8, xe2x80x9cStudy on Backplane Optics and Apply to Optical Data Busxe2x80x9d by Junji OKADA et al.
The optical data bus 50, which comprises a long plate of light transmissive material (for example, a light transmissive resin composed of an acrylic having a refractive index of 1.49 and an olefin polymer having a refractive index of 1.525, or the like), is a translucent transmission medium for transmitting signal light in the longitudinal direction by repetitive internal reflection.
Specifically, the optical data bus 50 comprises, as shown in FIGS. 6A and 6B, an approximately rectangular substrate of light transmissive resin having one longitudinal side thereof formed into a step-wise configuration, the steps being dimensioned such that light emitting elements (e.g. laser diode LD) or light receiving elements (e.g. photo diode PD) can be arranged from the side of one longitudinal end toward the other end. Signal light incoming/outgoing areas 52 are formed by sloping each longitudinal end of each of the steps at 45 degrees in relation to the surface of the substrate. FIG. 6A is a plan view of the optical data bus 50 and FIG. 6B is a side view thereof.
To perform optical transmission using the optical data bus 50, a reflective diffusion portion (e.g. light diffusive film) 54 is provided on the end surface opposite to the signal light incoming/outgoing areas 52 of the optical data bus 50 so that the optical data bus 50 has the diffusion angle in the thickness direction of 0.2 degrees and the diffusion angle in the width direction of 40 degrees. In addition, a laser diode LD or a photo diode PD is disposed above each of the signal light incoming/outgoing areas 52 such that each optical axis intersects perpendicularly to the substrate surface of the optical data bus 50.
Once the laser diode LD disposed above a given signal light incoming/outgoing area is activated and laser beam is irradiated from above the optical data bus 50, the entering light is totally reflected from the end surface sloped at 45 degrees in relation to the substrate surface of the optical data bus 50 and transmitted toward the reflective diffusion portion 54, then reflected and diffused from the reflective diffusion portion 54. The reflected light, in turn, is totally reflected from the end surface of each signal light incoming/outgoing area 52 and emitted from the top surface of the optical data bus 50. Thus, the optical signal emitted from the laser diode LD is transmitted to the photo diode PD disposed above the signal light incoming/outgoing area 52, with the result that the signal transmitted through the laser diode LD and the optical data bus 50 can be obtained from the current flowing through the photo diode PD.
Therefore, if a back plane board including the above described optical data bus as a signal transmission medium is put into practical use, it is possible to achieve interconnection, with a simple configuration, of a plurality of circuit boards provided with at least one of light emitting means comprising an electronic circuit for generating an electrical signal and a light emitting element for converting the electrical signal to an optical signal, and light receiving means comprising a light receiving element for converting an optical signal to an electrical signal and an electronic circuit for processing the converted electrical signal.
The use of the above described optical data bus as a signal transmission medium, however, presents problems of how to fix the optical data bus. Specifically, it is required to relatively position the optical data bus, the light emitting element and the light receiving element such that light is totally reflected from the signal incoming/outgoing areas and an optical signal is transmitted by repetitive internal reflection through the optical data bus, which is a translucent transmission medium. Also, since optical transmission in the optical data bus utilizes the air having a refractive index of 1 as a cladding layer, it is preferable not to use an adhesive for fixing the optical data bus. Further, since the optical signal totally reflected from the signal light incoming/outgoing area is required to be reflected and diffused from the other end of the optical data bus, a reflective diffusion portion such as a light diffusion film needs to be provided to the optical data bus in an appropriate manner.
However, there has not been provided any appropriate fixing means in order to use, as a signal transmission medium, an optical data bus having a step-wise configuration, as shown in FIGS. 6A to 6C. Therefore, an optical data bus fixing device which enables efficient transmission of an optical signal using an optical data bus is in demand.
The object of the present invention, which was meant to meet the demand, is to provide an optical data bus fixing board suitable for using the above described optical data bus as a signal transmission medium and an optical back plane board utilizing the optical data bus fixing board.
An optical data bus fixing board according to the present invention comprises a flat plate provided with a recess for insertion of an optical data bus opened corresponding to the surface configuration of the optical data bus and a positioning portion for positioning a light emitting element or a light receiving element in relation to each signal light incoming/outgoing area of the optical data bus inserted into the recess for insertion of an optical data bus, and is adapted such that the optical data bus inserted into the recess for insertion of an optical data bus in the flat plate is held by a first holding member provided on the longitudinally opposite side to each signal light incoming/outgoing area.
Therefore, the optical data bus can be fixed onto the optical data bus fixing board according to the present invention without using an adhesive. This enables the air having a refractive index of 1 to be used as a cladding layer of the optical data bus and decrease of the optical transmission efficiency in the optical data bus is prevented.
Also, since the light emitting element and the light receiving element can be positioned in relation to each of the signal light incoming/outgoing areas by using the positioning portions, the relative positions of these elements and areas can be set quite easily and precisely so that the light is totally reflected from the signal light incoming/outgoing areas.
The first holding member is provided with a reflective diffusion plate for abutting the end surface opposite to each of the signal light incoming/outgoing areas of the optical data bus and for reflecting the light entering through one of the signal light incoming/outgoing areas to the other signal light incoming/outgoing areas. By using the optical data bus fixing board according to the present invention, it is unnecessary to previously form a reflective diffusion portion at the end surface opposite to each of the signal light incoming/outgoing areas of the optical data bus. This not only simplifies production of an optical data bus, but also optimizes the reflective diffusion characteristics of light in the optical data bus since it is unnecessary to bond a reflective diffusion portion onto the optical data bus.
When a reflective diffusion portion, which is for reflecting and diffusing light at desired angles using the minute unevenness of its surface, is previously formed on an optical data bus, an adhesive is usually used. In this case, however, the unevenness is attenuated by the use of the adhesive and light cannot be reflected and diffused such that desired characteristics are obtained.
According to the present invention, wherein the first holding member is provided with the reflective diffusion plate which is adapted to abut the end surface of the optical data bus when the optical data bus is fixed onto the optical data bus fixing board, the light entering from one of the signal light incoming/outgoing areas can be reflected and diffused with desired characteristics. This enables the light emitted from the light emitting element to be surely transmitted to the light receiving element disposed above the signal light incoming/outgoing area.
The flat plate constituting the main body of the optical data bus fixing board may be made of resin, metal or a printed circuit board. In the case where a printed circuit board is employed, it is possible to form a power supply line and an electrical signal transmission line, or to mount electronic components constituting various signal processing circuits on the optical data bus fixing board In other words, the usability of the optical data bus is improved. Even the flat plate made of resin or metal, however, will have the same advantage if the flat plate is adapted such that the above mentioned lines can be formed thereon or a printed circuit board on which electronic components are mounted can be attached thereto.
When the flat plate is made of a printed circuit board, the board may be, for example, a multilayer board wherein a hole is provided in part of the stacked layers to form the recess for insertion of an optical data bus. The flat plate may be made of metal, but preferably is made of resin instead of metal because the difference of thermal expansion coefficient between a metal plate and the optical data bus is relatively large compared with a resin plate and therefore a metal plate is prone to damage the optical data bus.
The flat plate constituting the main body of the optical data bus fixing board may be provided with either a single recess for insertion of an optical data bus or a plurality of recesses for insertion of an optical data bus. When a plurality of recesses for insertion of an optical data bus are formed in the flat plate, a plurality of optical data buses may be installed on the common fixing board, which improves the operating efficiency in fixing the optical data buses in a device which uses a plurality of optical data buses as a signal transmission medium.
The plurality of recesses for insertion of an optical data bus are to be formed in the flat plate such that the signal light incoming/outgoing areas of the optical data buses are aligned on an orthogonal grid when the optical data buses are inserted into the recesses for insertion of an optical data bus.
Then, the light emitting elements or the light receiving elements can be disposed toward the respective signal light incoming/outgoing areas of a plurality of optical data buses by arranging the respective elements on the orthogonal grid. As described in the following embodiment, element holders holding respective elements and relatively positioned on the optical data bus fixing board may all be standardized.
When the plurality of recesses for insertion of an optical data bus are formed such that the signal light incoming/outgoing areas of the optical data buses inserted into the recesses for insertion of an optical data bus are aligned on the orthogonal grid, the flat plate (in other word, the optical data bus fixing board) is preferably formed into a rectangular so that the orthogonal grid lines are parallel or perpendicular to the side walls of the flat plate.
Thus, the above mentioned element holders may be aligned along the outer shape of the flat plate when fixed onto the optical data bus fixing board, and therefore it is easy to confirm whether or not the relative position of the element holder (i.e. the light emitting element or the light receiving element) relative to the optical data bus fixing board (i.e. the signal light incoming/outgoing area of the optical data bus) is precise, then positioning of respective portions is properly performed.
The first holding member, which is required to hold the end of the optical data bus opposite to each of the signal light incoming/outgoing areas, may be constituted to press the end from above the board, but preferably is constituted to press and bias the reflective diffusion plate against the end surface of the optical data bus using an elastic member. This enables fixation of the reflective diffusion plate to the optical data bus and, at the same time, fixation of the optical data bus within the recess for insertion of an optical data bus.
The elastic member for pressing and biasing the reflective diffusion plate against the end surface of the optical data bus may be a buffer material, such as rubber, or a spring, such as a flat spring or a coil spring. Since the reflective diffusion plate needs to be securely abuttingly fixed to the end surface of the optical data bus without being influenced by oscillation or thermal expansion (or shrinkage) of the optical data bus, the elastic member is more preferably one or more coil springs whose compressive force causes the reflective diffusion plate to be pressed and biased against the end surface of the optical data bus.
The optical data bus, which is made long, may come off the recess for insertion of an optical data bus even when one end of the optical data bus is held by the first holding member. Therefore, it is more preferable to provide a second holding member for holding the optical data bus inserted into the recess for insertion of an optical data bus on a side wall of the optical data bus along the longitudinal direction.
The second holding member, which is required to hold the optical data bus on the side wall thereof, may be constituted, for example, to press an end portion of the side wall from above the board. It is more preferable, however, that the second holding member is constituted to press and bias the side wall of the optical data bus by an elastic member, for the second holding member of this type can be formed with a simple structure and, in addition, the side wall of the optical data bus opposite to the second holding member is caused to abut the inner wall of the recess for insertion of an optical data bus and the optical data bus is securely held within the recess for insertion of an optical data bus.
In this case, the elastic member may be a buffer material, such as rubber, or a spring, such as a flat spring or a coil spring. In view of the function of the second holding member that it presses and biases on the longitudinal side wall of the long optical data bus, it is preferable to employ a flat spring which can bring its surface into contact with the side wall of the optical data bus and bias the side wall.
Since the second holding member needs to hold the long optical data bus on the longitudinal side wall thereof, the optical data bus can be held more securely when a plurality of the second holding members are provided for one optical data bus.
The recess for insertion of an optical data bus, which only needs to receive the optical data bus, may have approximately the same configuration as the optical data bus. It is preferable, however, that the configuration of the recess for insertion of an optical data bus is larger than the configuration of the optical data bus. This prevents the optical data bus from interfering with the recess for insertion of an optical data bus even when the optical data bus expands due to, for example, a thermal change in the ambient atmosphere, and also improves operating efficiency when the optical data bus is inserted into the recess for insertion of an optical data bus.
However, when the configuration of the recess for insertion of an optical data bus is larger than the configuration of the optical data bus, it becomes difficult to properly position the optical data bus (i.e. respective signal light incoming/outgoing areas) on the flat plate (i.e. the optical data bus fixing board). Accordingly, it is preferable to previously form a positioning projection on a side wall of the optical data bus and an engaging portion corresponding to the positioning projection in the side wall of the recess for insertion of an optical data bus along the longitudinal direction of the optical data bus.
Another aspect of the present invention relates to an optical back plane board comprising the above described optical data bus fixing board and the optical data bus inserted into the recess for insertion of an optical data bus of the optical data bus fixing board. The use of the optical back plane board, wherein the optical data bus is fixed onto the optical data bus fixing board according to the present invention, enables considerably simple connection between a plurality of circuits using the optical data bus as a signal transmission medium, once the light emitting elements and the light receiving elements (specifically the element holders) are positioned by using the positioning portions formed in the optical data bus fixing board.
Therefore, the optical back plane board facilitates achievement of information processing unit including a parallel architecture which supports speeding up of transmission and enables interconnection of multiple nodes with a simple architecture.